A shunt reactor is an inductive device which has an important function of compensating capacitive generation in a high voltage power transmission system. In a gapped core type of reactor a subdivided core leg comprising magnetic core elements is provided inside the reactor winding. This core leg functions as a carrier and director of the magnetic flux, thereby enabling high energy density and an advantageous operation of the reactor at higher system voltages.
A conventional core leg comprises a stack of magnetic core elements separated by spacer elements such as ceramic spacers. The core elements may be in the form of cylindrical segments of laminated core steel sheets, and the material of the spacer elements may be steatite or alumina. Typical spacer elements are cylinder-shaped and fill the core gaps to approximately 50-60%, but also hexagonal spacers have been suggested which fill the core gaps to a greater extent. The spacers may be bonded to the core elements with epoxy to form a rigid core leg.
The manufacturing of a core leg with a construction as described above requires high precision and a considerable amount of craftsmanship. When the ceramic spacers are bonded onto the core steel cylinder with epoxy, the tops of the spacers are planed to ensure an even surface before stacking the next core element. The machining of the ceramic spacers is difficult and expensive, and assemblage of the core leg segment by segment is very time-consuming. Moreover, the great number of manual manufacturing steps is leading to decreased precision of the construction causing increased sound level of the reactor and deformation of the gaps and core elements during operation. From the sound level point of view, it would also be desirable to increase the rigidity of the core leg.
One example of a gapped core leg construction is known from CA1034646, wherein the use of hard spacer material such as Micarta®, which is a composite of linen or paper fabric in a thermosetting plastic, is suggested.
JP58128709 discloses a core leg spacer in form of a disc having a diameter corresponding to that of the core elements. The spacer disc consists of resin-impregnated fibres, and the use of this type of spacer is aimed at facilitating the assembly of a shunt reactor core leg. A problem with using a large disc as a spacer is that it is difficult to get the mating surfaces of the disc and the core elements to match perfectly.